Make lost context callback a base::Closure thru the WGC3DProvider.

third_party/WebKit/public/platform/callback/WebClosure.h

Index: third_party/WebKit/public/platform/callback/WebClosure.h
diff --git a/third_party/WebKit/public/platform/callback/WebClosure.h b/third_party/WebKit/public/platform/callback/WebClosure.h
new file mode 100644
index 0000000000000000000000000000000000000000..6de6aa5f586995fbc5a37571374c0ad26b333c92
--- /dev/null
+++ b/third_party/WebKit/public/platform/callback/WebClosure.h
@@ -0,0 +1,72 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef WebClosure_h
+#define WebClosure_h
+
+#include "base/bind.h"
+#include "base/callback.h"
+#include "base/callback_helpers.h"
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "public/platform/WebCommon.h"
+
+#include <utility>
+
+#if BLINK_IMPLEMENTATION
+#include "wtf/Functional.h"
+#else
+#include "base/logging.h"
+#endif
+
+namespace blink {
+
+// Conversion from WTF closures to base closures to pass a callback out of
+// blink.
+class WebClosure {
+public:
+#if BLINK_IMPLEMENTATION
+    WebClosure() {}
+
+    explicit WebClosure(PassOwnPtr<SameThreadClosure> c)
+    {
+        auto run_and_delete = +[](scoped_ptr<SameThreadClosure> c)

[Ken Russell (switch to Gerrit), 2016/03/24 18:29:04]

Is the "+" strictly needed to avoid compile errors?
http://stackoverflow.com/questions/17822131/resolving-ambiguous-overload-on-f...

[danakj, 2016/03/24 18:36:50]

The + let's bind work. Bind won't let you use a lambda, but it can take a
function pointer.

[danakj, 2016/03/24 18:38:09]

But apparently does not work in MSVC. Cool.

+        {
+            (*c)();
+        };
+        m_closure = base::Bind(run_and_delete, base::Passed(make_scoped_ptr(c.leakPtr())));
+    }
+#endif
+
+    // TODO(danakj): These could be =default with MSVC 2015.
+    WebClosure(WebClosure&& other) { *this = std::move(other); }
+    WebClosure& operator=(WebClosure&& other)
+    {
+        m_haveClosure = other.m_haveClosure;
+        other.m_haveClosure = false;
+        m_closure = std::move(other.m_closure);
+        return *this;
+    }
+
+#if !BLINK_IMPLEMENTATION
+    // TODO(danakj): This could be rvalue-ref-qualified.
+    base::Closure ToBaseClosure()
+    {
+        // Don't call this more than once!
+        DCHECK(m_haveClosure);
+        m_haveClosure = false;
+        return std::move(m_closure);
+    }
+#endif
+
+private:
+    bool m_haveClosure = true;
+    base::Closure m_closure;
+
+    DISALLOW_COPY_AND_ASSIGN(WebClosure);
+};
+
+} // namespace blink
+
+#endif // WebClosure_h